JP2006509214A - Backflow prevention for high pressure gradient systems - Google Patents

Abstract

The gradient performance of the high pressure gradient solvent delivery system is optimized by approximating the infinite stroke volume of the high pressure pumps 105, 122 by adding pulse dampening with backflow prevention to each high pressure pump 105, 122. This backflow prevention adds sufficient minimum flow resistance, which improves pulse dampening performance over a wider range of flow rates and provides consistent gradient performance.

Description

  This application claims the priority of patent provisional application No. 10/314725 filed on Dec. 9, 2002.

  The present invention relates to liquid chromatography devices and solvent delivery systems, and more particularly to a method and apparatus for controlling a chromatography pump system.

  High pressure liquid chromatography (HPLC) solvent delivery systems can be used from substantially atmospheric pressure, often 10,000 pounds per square meter, of a single component liquid or mixture of liquids (both known as “mobile phases”). Used as a source at pressures that can range up to pressures on the order of inches. These pressures are required to push the mobile phase through the fluid path of the stationary phase support, thereby allowing separation of dissolved analytes. The stationary phase carrier may comprise a packed bed of particles, a membrane or membrane assembly, a porous monolithic bed, or an open tube. In many cases, the analysis conditions require the mobile phase composition to change during the analysis (this mode is referred to as “gradient elution”). In gradient elution, the viscosity of the mobile phase can change and the pressure required to maintain the required measured volume flow will change accordingly.

  In liquid chromatography, as a result of selection of an appropriate separation strategy (including hardware, software, and chemistry), the injected sample mixture is separated into its components, which are reasonably different zones or “bands”. ) "To elute from the column. As these bands pass through the detector, their presence can be monitored and a detector output (usually in the form of an electrical signal) can be generated. The analyte concentration pattern inside the elution band can be represented by a time-varying electrical signal, leading to the nomenclature “chromatography peak”. A peak may be characterized in relation to its “retention time”, which is related to the time of injection (ie, the time of injection is equal to zero) and the center of the band is the detector Is the time to pass through. In many applications, the peak retention time is used to estimate the identity of the eluting analyte based on related analysis with standards and calibrators. The retention time of the peak is strongly influenced by the mobile phase composition as well as the cumulative volume of mobile phase that has passed over the stationary phase.

  The practicality of chromatography can be analyzed in a set of runs with standards and calibrators so that the data obtained can be trusted, followed by test samples or unknowns followed by more The standard is highly dependent on the reproducibility of run-to-run that allows the standard to be analyzed. Known pump systems exhibit some non-ideal characteristics, resulting in reduced separation performance, as well as reduced run-to-run reproducibility. Among the non-ideal pump characteristics exhibited by known pump systems are generally solvent composition fluctuations and / or measurement volume flow fluctuations.

  Measurement volume flow fluctuations present in known HPLC pump systems are disadvantageous because the retention time (s) for a given analyte may vary. That is, the amount of time that the analyte is retained in the stationary phase results in undesirable fluctuations as a function of undesirable measurement volume flow fluctuations. This creates difficulties in estimating the identity of the sample from the retention behavior of its components. Measurement volume flow fluctuations from individual pumps can cause fluctuations in the solvent composition when adding the output of multiple pumps to provide a solvent composition.

  Fluctuations in the solvent composition present in known HPLC pump systems have the disadvantage of interacting with the system's analyte detector and causing the detected disturbance as if it were caused by the presence of the sample. is there. In practice, an interference signal is generated. This interference signal is added to the actual signal due to the analyte, which causes an error in calculating the amount of unknown sample from the area of the eluted sample peak.

  The prior art provides techniques and apparatus implementations aimed at controlling solvent delivery and minimizing the disturbance of the delivery system output for the analytical device. A number of pump configurations are known that allow fluid to be transmitted at high pressures for use in applications such as liquid chromatography. Known pumps, such as the pump disclosed in US Pat. No. 4,883,409 (“the '409 patent”), have at least one plan that reciprocates inside a pump chamber into which fluid is introduced. Incorporates a jar or piston. The flow rate of fluid output from the pump is determined by the frequency and stroke length of the controlled reciprocating movement of the plunger within the pump chamber. However, the assembly for driving the plunger is carefully combined with elements, which can introduce undesirable movement into the plunger when the plunger is driven, which can cause solvent delivery system output. This makes it difficult to precisely control the noise and causes what is called “noise”, ie, a detectable disturbance of the chromatographic baseline. Much of this noise is not due to random statistical fluctuations in the system, many of which are a function of the pump's mechanical “signature”. Mechanical signatures are mechanical related, such as ball / screw drives, gears and / or other component anomalies used in pumps that produce linear motion that drives the piston (s). It correlates with a phenomenon or relates to a high level process or physical phenomenon such as the start or completion of solvent compression or the start of solvent transfer from a pump chamber.

  Known typical systems for transferring liquids in liquid chromatography applications, such as those disclosed in the '409 patent, or even in US Pat. No. 5,393,434, are reciprocal plans. A dual piston pump having two interconnected pump heads with jars is realized. The plunger is driven by a predetermined phase difference to minimize output flow fluctuations. The stroke length and stroke frequency of the piston can be adjusted independently when the piston is independently driven synchronously. In order to compensate for various fluid compressibility in an effort to maintain a substantially constant system pressure and output flow rate, each pump cylinder can be pre-compressed in any given pump cycle. .

  There are two widely used means for creating gradient HPLC pumps. The solvent can be blended on the intake side of the pump. This is known in the art as low pressure gradient mixing. Another is to use a so-called high pressure gradient system in which each individual solvent is transmitted by a separate pump.

  The basic scalar for all forms of gradient chromatography is the void volume of the separation column. The void volume of an HPLC column is the sum of the interparticle and intraparticle volumes of the column filled with mobile phase. This void volume is the minimum volume required to elute unretained solutes. The gradient delay volume is the volume of mobile phase that is transmitted from the time the gradient is initiated to the time the composition change first reaches the column position. Delay volume is the metered volume overhead of the gradient solvent delivery system, which adds to the time required to complete the separation and prepare the column for the next injection. The lag volume should be minimized and ideally not more than twice the void volume of the column.

  When two or more high pressure pumps are combined to form a gradient solvent delivery system, the synthesis of these outputs results in fluid crosstalk between the high pressure pumps during individual piston crossovers. there is a possibility. One conventional way to avoid fluid crosstalk is to use a pulse dampener inside a gradient solvent delivery system as shown in FIG.

  If the individual pulse dampener is located upstream of the point where the solvent output meets and the total flow is small compared to the volume of the pulse dampener, the two pumps will have their respective piston crossovers. There will be a significant amount of crosstalk between these pumps because they are not synchronized with respect to each other. This crosstalk occurs because the fluid contained within the off-line pulse dampener is subject to compression, which can be a low impedance path for an on-line pump. For this reason, a compromise between the flow rate and the composition can be obtained by arranging the pulse dampener upstream. The fluidic crosstalk results are depicted in FIG. 2, which plots the transfer of gradient markers from a low flow solvent delivery system configured as shown in FIG. As shown in FIG. 2, none of the gradient transmissions are identical and none of these correspond to the programmed gradient. This results in an unsatisfactory and unpredictable separation that cannot be reproduced.

  In another prior art scheme, a capillary restrictor is used to generate a counter pressure to operate the pulse dampener. A capillary with a fixed length and inner diameter provides sufficient counterpressure for suppression over a narrow range of flow rates, but unfortunately does not prevent backflow.

  Yet another approach for the use of pulse dampener is to position the pulse dampener downstream of a common mixing tee. This approach is useful in large volume gradient systems, but becomes problematic when the volume scale is smaller. By positioning the pulse dampener behind the common mixing tee, the delay volume inside the gradient system is greatly increased. Pulse dampeners typically scale to a certain limited flow range to combine the resistance to flow and the constrained receiving volume of the mobile phase. Effective pulse dampening requirements and delay volume minimization are in conflict in reducing the size of the HPLC system with respect to column volume and instrument volume flow.

  The present invention provides an improved method and apparatus for improving the composition accuracy of high pressure gradient pumps for HPLC by approximating an infinite stroke volume by backflow prevention pulse dampening. Backflow prevention according to the present invention adds sufficient minimum flow resistance, which improves pulse dampening performance over a wider range of flow rates and provides consistent gradient performance.

  In accordance with the present invention, the stored mobile phase is compressed during the transmission cycle by linking the pulse dampener as a check valve or with a backflow preventer that may be embodied as a backpressure regulator in the line. Is guaranteed. If a backflow preventer with a fixed minimum flow resistance is used, the effectiveness of the pulse dampener is substantially independent of the flow rate. By utilizing a backflow preventer in the gradient system, it is ensured that the stored mobile phase has mechanical energy that undergoes compression and returns to the system at the piston crossover position.

  The backflow preventer further ensures that the outflow check valves of the respective pump heads receive sufficient backpressure to enable their proper function. This sufficient back pressure is particularly useful in systems where the flow rate is low when the back pressure generated by the columns and capillaries is limited. In addition, the counter pressure allows more consistent operation of the primary check valves of the individual pumps because the resulting counter pressure ensures proper installation of the outflow check valve on the pump head that is offline.

  With the proper arrangement of the backflow preventer according to the invention, the fluid crosstalk is reduced, the performance of the in-line pulse damper is optimized and the performance of the high pressure pump is improved, which is A plot of gradient marker transmission from a solvent delivery system configured to provide prevention is shown in FIG. As shown in FIG. 3, the gradient transmission is identical to and corresponds to the programmed gradient.

  A separate pump is advantageous because a smooth flow is transmitted by the addition of an appropriate pulse dampener with the additional use of a backflow preventer to prevent fluid crosstalk between the two mobile phases. is there. Since a pulse dampener is fluidly equivalent to a low-pass filter, when a small stroke volume is combined with a pulse dampener, a crossover disturbance occurs at frequencies that are subject to strong attenuation. Differences between individual pump heads are effectively averaged by the use of a pulse dampener. Thus, utilizing a small stroke volume together with efficient pulse dampening provides a uniform formulation of the solvent in the high pressure gradient system.

  In an alternative exemplary embodiment, a capillary restrictor is utilized to generate a counter pressure to operate the pulse dampener. Sufficient back pressure is provided over a range of flow rates by a capillary having a fixed length and inner diameter. In systems with a consistent flow rate, a capillary restrictor can be used in series with the check valve.

  In yet another alternative exemplary embodiment, the check valve is incorporated into a mixing tee. This incorporation reduces the volume of the mobile phase inside the gradient system, thereby reducing the delay volume of the gradient system.

  The foregoing features and advantages of the present invention, as well as other features and advantages, will be more fully understood from the following detailed description of exemplary embodiments taken in conjunction with the accompanying drawings.

  Although the present disclosure will be described in detail with respect to chromatographic applications, it should be understood that embodiments of the present invention are also intended for industrial and process control applications.

  As shown in FIG. 4, the effect of pump crossover on solvent composition is illustrated. In this illustration, the total flow is 1 mL / min. The first pump delivers 90 percent of this flow, ie approximately 900 μL / min. The second pump delivers 10 percent of this flow, ie approximately 100 μL / min. The stroke volume is approximately 100 μL for both these pumps. There are nine crossovers of the first pump relative to one crossover of the second pump to provide the desired composition. When the first pump crosses over, the first solvent is deficient in about 23 percent of the flow rate and the composition is instantly concentrated in the second solvent. This deficiency is represented by the first curve 301. The second curve 302 represents the effect of using limited pulse dampening to reduce the amount of underflow from about 23 percent flow loss at the crossover location to 10 percent flow loss. The compositional disturbance or “noise” drops from about ± 3 percent of the transmitted second solvent to about ± 1 percent of the transmitted second solvent. The additional pulse dampening according to the present invention further reduces the composition noise.

The influence of the composition noise on the retention time of the sample peak depends strongly on the degree of retention of the sample, and is expressed by the k prime value (k ′ value) corresponding to the number of column volumes required for elution of the sample from the column. Is done. The k ′ value is calculated from the following equation.
k ′ = (V _r −V ₀ ) / V ₀ (Formula 1)
In the above formula, V _r = retention volume and V ₀ = column void volume.

  Since k ′ is exponentially proportional to the percentage of the second solvent to which it is transmitted, the change in mobile phase composition has a small effect on the retention volume when k ′ is small, but the movement when k ′ is large. Small variations in phase composition have a significant effect on the retention volume.

  The cumulative effect of pump crossover on the transmitted percentage of the second solvent is illustrated in FIG. This cumulative error expressed as a percentage of the second solvent is strongly related to the magnitude of the gradient pulse. The resulting retention time dispersion is strongly related to the degree of pulsing, and the mixing requirements that ensure a more uniform composition are directly related to the instantaneous and cumulative errors expressed as a percentage of the second solvent. The When pulsing is reduced according to the present invention, the composition becomes essentially more uniform and the volume required to ensure uniformity is smaller.

  Turning to FIG. 6, an exemplary embodiment of the present invention is a high pressure gradient system in which each individual solvent is transmitted by a separate pump. This exemplary embodiment has a first solvent transfer line 101 and a second solvent transfer line 103. The first solvent is transmitted to the first pump 105 inside the first solvent transmission line 101 via the fluid T joint 104. The first pump 105 has a first piston 107 and a second piston 109. In this exemplary embodiment, the first pump 105 is a Waters model HPLC pump 515 manufactured by Waters Corporation (Milford, Mass.), A fluid pump with a fixed stroke length. It is contemplated that other pumps known in the art can be utilized and are within the scope of the present invention.

  The first solvent is Waters P / N WAT 207085 (Waters Corporation, Massachusetts) which also serves as a fluid T-joint that receives the output from the first piston 107 and the second piston 109 via the first pump 105. Is transmitted to a prime valve 111 such as Milford)). The first solvent is transmitted to the first pulse dampener 112. In this exemplary embodiment, the first pulse dampener 112, which is a Waters High Pressure Filter (P / N WAT 207072 (Waters Corporation, Milford, Mass.)), Is responsible for the flow disturbance within the first solvent transmission line. A fluid low-pass filter to minimize. It is contemplated that other pulse dampeners known in the art can be utilized and are within the spirit of the invention.

  The first solvent is pumped through the first pulse dampener 112 and transmitted to the first backflow preventer 114. In this exemplary embodiment, the first backflow preventer 114, which is Upchurch Model U-609 (Upchurch Scientific, Oak Harbor, WA), is configured to ensure consistent operation of the first pulse dampener 112. One pulse dampener 112 has a known resistance to the flow force that creates a load. This resistance to flow can range from about 0 psi to 2,000 psi, and in this first exemplary embodiment, the resistance is approximately 250 psi.

  The first backflow preventer 114 is a common mixing tee 116 and fluid that directs the first solvent through a pressure transducer 118 into a vent valve 119, such as Rheodyne 7033 (Rheodyne, LP. (Rohnert Park, Calif.)). Communicate. Vent valve 119 conducts the first solvent to the injector and chromatography column 120.

  The second solvent is transmitted to the second pump 122 inside the second solvent transmission line 103 via the second fluid T joint 124. The second pump 122 has a first piston 124 and a second piston 126. In this exemplary embodiment, the second pump 122 is a Waters model HPLC pump 515 (Waters Corporation, Milford, Mass.), Which is a fluid pump with a fixed stroke length. It is contemplated that other pumps known in the art can be utilized and are within the spirit of the invention.

  The second solvent is a Waters P / N WAT 207085 (Waters Corporation, Mil, Mass.) That also serves as a fluid T-joint that receives output from the first piston 124 and the second piston 126 via the second pump 122. Ford)) or the like is transmitted to a second prime valve 128. The second solvent is transmitted to the second pulse dampener 130. The second pulse dampener 130 provides a fluid low pass filter that minimizes flow disturbance within the second solvent transmission line. The second solvent is pumped to the second backflow preventer 132. The second backflow preventer 132 is a resistance known to the flow force that creates a pressure load on the second pulse dampener 130 to ensure consistent operation of the second pulse dampener 130. have. This resistance to flow can range from 0 psi to 2,000 psi, and in this first exemplary embodiment, the resistance is approximately 250 psi.

  The second backflow preventer 132 is a common mixing tee that directs the first solvent through the pressure transducer 118 into the relief valve 119 and directs the second solvent 102 through the pressure transducer 118 into the relief valve 119. 116 is in fluid communication. A relief valve 119, such as Rheodyne 7033 (Rheodyne, LP. (Rohnert Park, Calif.)), Directs the first solvent 101 and the second solvent 102 to the chromatography column 120.

  In an alternative embodiment of the invention, the first backflow preventer and the second backflow preventer are incorporated into the structure of the mixing T-joint to minimize system volume. As shown in FIG. 7, a common mixing T-joint 201 has a first backflow preventer 203 and a second backflow preventer 205 incorporated in the structure of the mixing T-joint 201. The mixing T-joint 201 includes a first inlet 207 into which the first backflow preventer 203 is incorporated, a second inlet 215 into which the second backflow preventer 205 is incorporated, a first inlet 207 and And an outlet 214 through which a fluid flow from the second inlet 215 is guided.

  The first backflow preventer 203 has a first ball bearing 211 housed in the first check valve body 220. The first ball bearing 211 is mounted in a first check valve seat 213. The first ball bearing 211 is made of a material that is inert to the system solvent, such as sapphire or ceramic. The first ball bearing 211 is housed in the first check valve cartridge housing component 221 in a manner that allows only forward fluid flow. The first check valve cartridge housing component 221 comprises a top portion 222 and a base portion 224 and forms a first check valve seat 213.

  The second backflow preventer 205 has a second ball bearing 217 accommodated in the second check valve body 223. The second ball bearing 217 is mounted in the second check valve seat 218. The second ball bearing 217 is made of a material that is inert to the system solvent, such as sapphire or ceramic. The second ball bearing 217 is housed in the second check valve cartridge housing component 227 in a manner that allows only forward fluid flow. The second check valve cartridge housing component 227 comprises a top portion 229 and a base portion 226 and forms a second check valve seat 218.

  In yet another alternative embodiment of the present invention, the first backflow preventer and the second backflow preventer are incorporated within the structure of the mixing tee to minimize system volume. As shown in FIG. 8, the common mixing T joint 301 has a first backflow preventer 303 and a second backflow preventer 305 incorporated in the structure of the mixing T joint 301. The mixing T-joint 301 includes a first inflow port 307 in which a first backflow preventer 303 is incorporated, and a second inflow port 315 in which a second backflow preventer 305 is incorporated. , And an outlet 314 to which a fluid flow from the first inlet 307 and the second inlet 315 is guided.

  The first backflow preventer 303 has a coil spring 309 that applies pressure to the first actuator 311. The first actuator 311 is attached to the inside of the first valve opening 313. The selected coil spring 309 provides some resistance to the flow by exerting pressure on the first actuator, thereby sealing the first valve opening 313 until the resistance to the flow is exceeded. It has stopped.

  The second backflow preventer 305 has a coil spring 316 that applies pressure to the second actuator 317. The second actuator 317 is attached inside the second valve opening 318. Again, the selected coil spring 316 provides some resistance to the flow by exerting pressure on the second actuator 317, thereby causing the second coil until the resistance to the flow is exceeded. The valve opening 318 is sealed.

  In yet another alternative embodiment, the pulse dampener inside the fluid solvent transmission line is made up of a section of capillary that is optimized for its length and diameter, thereby providing the required volume inside the capillary. The flow disturbance is minimized.

  While the chromatography pump operating system described in the exemplary embodiments herein is configured to accommodate two separate solvent sources, multiple or single as known in the art. It should be understood that a solvent delivery system can be implemented.

  While the chromatography pump operating system described in the exemplary embodiments herein is configured to have a conventional actuator and spring backflow preventer, another backflow preventer as is known in the art. It should be understood that is also available.

  The foregoing describes specific embodiments of the method and apparatus of the present invention. The described exemplary embodiments are for purposes of illustrating specific aspects of the present disclosure, and the present disclosure is not intended to be limited in scope by the described exemplary embodiments. Equivalent methods and components are also within the scope of this disclosure. Indeed, those skilled in the art will appreciate that the present disclosure allows for various modifications and additional modifications to the exemplary embodiments. Such modifications are intended to fall within the scope of the appended claims.

1 is a diagram of a standard high pressure gradient pump (prior art). It is a figure showing the problem of the fluid crosstalk in a high pressure gradient system (prior art). It is a figure showing the influence of pump crossover with respect to the solvent composition (prior art) without backflow prevention. FIG. 2 is a diagram of a valve according to the present invention. It is a figure showing the cumulative influence of the pump crossover with respect to a solvent composition (prior art). 1 is a diagram of a high pressure gradient pump operating system according to the present invention. FIG. It is a figure of the mixing T joint incorporating the check valve. It is a figure of the mixing T joint incorporating a check valve and a back pressure regulator.

Claims (22)

A method for improving the composition accuracy of a high pressure gradient pump for high pressure liquid chromatography,
A first solvent line having a first set of pumps and a second solvent line having a second set of pumps, wherein the first set of pumps are in fluid communication with a first solvent reservoir and the second set of pumps; Providing the pump in fluid communication with the second solvent reservoir;
A second pump is connected to the first pulse dampener that is in fluid communication with the first backflow preventer and the second set of pumps is in fluid communication with the second backflow preventer. The backflow preventer substantially reduces fluidic crosstalk between the solvent lines; and
Connecting the backflow preventer to a mixing T-joint to transmit the solvent composition;
Including methods.   The method of preventing backflow according to claim 1, wherein the backflow preventer improves composition accuracy.   The method of backflow control according to claim 1, wherein the backflow preventer enables accurate composition transfer at a flow rate substantially smaller than the volume of the pulse dampener.   The method of backflow control according to claim 1, wherein the backflow preventer enables accurate composition transfer at a flow rate substantially equivalent to the discharge volume of each pump chamber of the pump.   The method of preventing backflow according to claim 1, wherein the backflow preventer is incorporated in the mixing tee so as to reduce a delay volume.   The method of preventing backflow according to claim 5, wherein the built-in backflow preventer includes a backpressure regulator.   2. The method of claim 1, further comprising providing a back pressure regulator having a fixed resistance selected to ensure that the pulse dampener functions efficiently with the consistent performance of the primary check valve of the pump. Backflow prevention method. A first set of pumps in fluid communication with the first purge valve and a second set of pumps in fluid communication with the second purge valve;
A first pulse dampener in fluid communication with the first backflow preventer and a second pulse dampener in fluid communication with the second backflow preventer;
A mixing T-joint in fluid communication with the backflow preventer and in fluid communication with a vent valve in fluid communication with the chromatography column;
A high pressure liquid chromatography apparatus comprising:   9. The backflow preventer comprises a backpressure regulator having a fixed resistance selected to ensure that the pulse dampener functions efficiently with the stability of the primary check valve of the pump. The backflow prevention device as described.   The backflow prevention device according to claim 8, wherein the accuracy of composition transmission is improved by the backflow preventer.   The backflow prevention device according to claim 8, wherein the backflow prevention device enables accurate composition transmission at a flow rate substantially equivalent to a discharge volume of each pump chamber of the pump.   9. The backflow prevention device according to claim 8, wherein the backflow preventer is incorporated in the mixing T-joint to reduce the delay volume.   The backflow prevention device according to claim 8, wherein the built-in backflow prevention device includes a back pressure regulator.   The backflow prevention device according to claim 8, wherein the backflow prevention device enables accurate composition transfer at a flow rate substantially smaller than the volume of the pulse dampener.   9. The backflow prevention of claim 8, wherein the pulse dampener reduces pump pulsing, thereby reducing the volume requirement for effective solvent mixing, allowing the use of a high pressure gradient system in smaller volume chromatography columns. apparatus. A first set of pumps in fluid communication with the first solvent reservoir in the first solvent transfer line and a second in fluid communication with the second solvent reservoir in the second solvent transfer line. A pair of pumps,
Means for pulse dampening to reduce flow disturbances generated by the first set of pumps and the second set of pumps;
Means for preventing backflow to eliminate fluidic crosstalk between the solvent transmission lines;
A high pressure liquid chromatography apparatus comprising:   The apparatus of claim 16, further comprising means for back pressure adjustment. A mixing T-joint having an outlet, a first inlet and a second inlet;
A backflow preventer incorporated within the first and second inlets, comprising a selected coil spring and actuator mounted within a valve seat, the selected coil spring comprising: A backflow preventer acting a selected pressure on the actuator;
A high pressure liquid chromatography apparatus comprising:   The high pressure liquid chromatography apparatus of claim 18, wherein the selected pressure is in the range between 0 psi and 2000 psi.   The high pressure liquid chromatography apparatus according to claim 18, wherein the system volume is reduced by the incorporation.   19. The high pressure of claim 18, wherein the backflow preventer has a fixed resistance selected to ensure that the pulse dampener in the chromatography system functions efficiently with the stability performance of the primary check valve of the system pump. Liquid chromatography device. A mixing T-joint having an outlet, a first inlet and a second inlet;
A backflow preventer incorporated within the first and second inlets, the backflow preventer having a ball bearing attached to the interior of the valve seat for restricting fluid flow in the forward direction; ,
A high pressure liquid chromatography apparatus comprising:

Images